/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.sanselan.formats.png;

import java.io.IOException;

import org.apache.sanselan.ImageReadException;

public class BitParser
{
	private final byte bytes[];
	private final int bitsPerPixel;
	private final int bitDepth;

	public BitParser(byte bytes[], int bitsPerPixel, int bitDepth)
	{
		this.bytes = bytes;
		this.bitsPerPixel = bitsPerPixel;
		this.bitDepth = bitDepth;
	}

	public int getSample(int pixelIndexInScanline, int sampleIndex)
			throws ImageReadException, IOException
	{
		int pixelIndexBits = bitsPerPixel * pixelIndexInScanline;
		int sampleIndexBits = pixelIndexBits + (sampleIndex * bitDepth);
		int sampleIndexBytes = sampleIndexBits >> 3;

		if (bitDepth == 8)
			return 0xff & bytes[sampleIndexBytes];
		else if (bitDepth < 8)
		{
			int b = 0xff & bytes[sampleIndexBytes];
			int bitsToShift = 8 - ((pixelIndexBits & 7) + bitDepth);
			b >>= bitsToShift;

			int bitmask = (1 << bitDepth) - 1;
			return b & bitmask;
		} else if (bitDepth == 16)
		{
			return (((0xff & bytes[sampleIndexBytes]) << 8) | (0xff & bytes[sampleIndexBytes + 1]));
		}

		throw new ImageReadException("PNG: bad BitDepth: " + bitDepth);
	}

	public int getSampleAsByte(int pixelIndexInScanline, int sampleIndex)
			throws ImageReadException, IOException
	{
		int sample = getSample(pixelIndexInScanline, sampleIndex);

		int rot = 8 - bitDepth;
		if (rot > 0)
			sample <<= rot;
		else if (rot < 0)
			sample >>= -rot;

		return 0xff & sample;
	}
}